% Listing 9-8 - Recursive root finding
 function pt = findZero(x)
% x is a lower-upper pair guaranteed to have
%                  y values of opposite sign
%     return the x coordinate of the root
 if abs(x(1)-x(2)) < .001
     pt = x(1);
 else
     mx = sum(x)/2;
     my = f(mx);
     if my*f(x(1)) <= 0
         pt = findZero([x(1) mx]);
     else
         pt = findZero([mx x(2)]);
     end
 end
